Research: Coral reefs’ decline actually began centuries ago

Global warming and pollution are among the modern-day threats commonly blamed for decline of coral reefs, but new research shows the downfall of those resplendent and diverse signatures of tropical oceans actually may have begun centuries ago.

According to a paper set to appear Friday (8/15) in the journal Science, the downward spiral started when people first began killing off reef-frequenting large fish, turtles, seals and other top predators or herbivores – a process that started thousands of years ago in some parts of the world and just a century or so ago in others.

“What really struck us was the universality of the decline trajectories,” said Karen Bjorndal, one of 12 authors on the paper and zoology professor and director of the Archie Carr Center for Sea Turtle Research at the University of Florida. “It didn’t matter if we were looking at the Red Sea, Australia or the Caribbean. As soon as human exploitation began, whether in the 1600s in Bermuda or tens of thousands of years ago in the Red Sea, the same scenarios were put into play.”

The project is an outgrowth of research published in 2001 that tied overfishing to worldwide declines of coastal ecosystems. That paper argued that overfishing disturbs the ecological balance of marine environments, with the killing of green sea turtles, for example, ultimately contributing to the die-off of sea grasses. The authors of the current paper, who were among the scientists involved in that research, zeroed in on coral reefs, long seen as seriously threatened by modern pollution, global warming and diseases that cause the coral organism to die and “bleach,” its mosaic of colors turning a uniform skeletal white. The goal: reconstruct the ecological history of the reefs from before the first people appeared to fish them some 40,000 years ago to the present era.

The scientists pored over historical and archaeological records surrounding major reef systems in 14 regions in the Atlantic and Pacific oceans and the Red Sea, including the reefs of the Caribbean and the Great Barrier Reef. Each scientist handled a different region, with Bjorndal tackling the Bahamas and the Cayman Islands. She said her research led her to more than 400 references for the Bahamas alone, including papers on archaeological findings and colonial fishing-catch records. Among her sources: research by UF anthropologists showing that indigenous Bahamians hunted green turtles to such an extent they seriously depleted the herbivore long before the first colonists arrived.

“I used to think that green turtles were basically in pristine shape when Columbus arrived, and I don’t think that anymore,” she said.

The researchers discovered that all the reefs experienced declines as a result of human activity, although the declines occurred over different periods of time and were more advanced in some places than others. Regardless of geography, the researchers learned, the declines follow the same pattern. First, people deplete large predators such as sharks and large herbivores, which tend to be both easy to kill or capture and slow to rebuild their populations. Next to go are smaller animals, such as small fishes, followed last by sea grasses, corals and other so-called “architectural” parts of the coral reefs.

By 1900 — decades before the first scuba divers experienced the splendor of coral reefs — this slow death had already started in more than 80 percent of the reefs worldwide, the scientists found. Today, in the regions where the process is most advanced, such as Jamaica, the corals are either dead or dying, the fish are tiny, few other organisms such as shellfish exist, and the formerly vibrant reef structure is dull and coated with algae. The Great Barrier Reef sometimes is said to be largely pristine, but it’s actually as much as a third of the way toward ecological extinction, Bjorndal said.

For the first time, Bjorndal said, the research will give managers of the world’s coral reefs – and the countries that have jurisdiction over these resources — a yardstick they can use to determine how far their particular reef system has progressed along the ecological “extinction continuum.” She and the other scientists hope the result will help spur strengthened conservation efforts. She noted that, with the exception of the extinct Caribbean monk seal and a handful of other top predators, most reef organisms have been depleted but are not yet extinct – offering at least some hope for the future.

“If we could step back in with strong management decisions we could restore the ecosystem, but that’s a matter of political will and funding and a lot of other influences that are difficult to predict,” she said.

Writer: Aaron Hoover, 352-392-0186, ahoover@ufl.edu
Source: Karen Bjorndal, 352-392-5194, kab@zoo.ufl.edu